ATLANTIC CITY – It’s an hour from kickoff ahead of the Week 4 NFL games, and inside the William Hill Sports Book in the Ocean casino, business is already booming. More than 60 people are waiting to place their NFL bets from one of the six tellers, and the line stretches out of the sports book, around a wall next to a row of Triple Digit Diamond slot machines.

Gamblers, mostly men, many of them wearing NFL jerseys and team garb, hold coffees and cocktails as they stare at printouts of the day’s NFL lines. There’s the Chargers, a 10.5-point home favorite against the Jimmy Garoppolo-less 49ers … that seems like an easy cover? Or the Indianapolis Colts, only a 1-point favorite against the winless Texans. What about the New England Patriots, a seven-point home favorite against the undefeated Miami Dolphins. Tom Brady couldn’t possibly lose three straight games, could he?

This is the new normal in Atlantic City on an NFL Sunday now that sports gambling is...